Synthesis of alkali metal hexahydroaluminate complexes using dimethyl ether as a reaction medium

A novel method of preparation of hexahydroaluminate complexes M₃AlH₆ (M = Li, Na or K) from the corresponding alkali metal hydride and tetrahydroaluminate has been explored, using dimethyl ether (Me₂O) as a solvent at near-ambient temperatures. The results are compared with those obtained using a recently established mechanochemical approach. Characterization of the products by powder X-ray diffraction revealed M₃AlH₆ to be formed in high yield for M = Li and Na, but not for M = K. The attempted preparation of Li₂NaAlH₆ and Li₂KAlH₆ was unsuccessful.     

Stability and solvation of alkali metal ion complexes with dibenzo-30-crown-10

Stability constants for the 1:1 complexes of dibenzo-30-crown-10 (DB30C10) with alkali metal ions have been determined at 25 °C in nitromethane and water by conductometry and capillary electrophoresis, respectively. Transfer activity coefficients of DB30C10 and its complexes from nitromethane to S (S = water, acetonitrile, propylene carbonate, methanol, and N,N-dimethylformamide) have been determined at 25 °C to evaluate the solvation properties. The stability constant in the poorly solvating solvent, nitromethane, decreases with increasing metal ion size, Na⁺ > K⁺ > Rb⁺ > Cs⁺, reflecting the intrinsic selectivity governed by electrostatic interaction between the metal ion and the ether oxygen atoms. It is also suggested that a part of the ether oxygen atoms does not bind to the metal ion in the Na(DB30C10)⁺ complex. The aqueous stability constant varies as Na⁺ ? K⁺ ≈ Rb⁺ ≈ Cs⁺; this selectivity pattern is similar to that in acetonitrile, propylene carbonate, and methanol. The complex stability in water is very low compared to that in the nonaqueous solvents, owing to hydrogen bonding of water to the oxygen atoms of the free crown ether. The transfer activity coefficient values show that DB30C10 shields all the metal ions effectively from the solvents and lead to the conclusion that the complexation selectivity in S receives a significant contribution from the solvation of the free metal ions. The Na(DB30C10)⁺ complex has specific interaction with water, causing much lower K⁺/Na⁺ selectivity in H₂O than in MeOH.     

Effects of counter-ion size on solid state structures of M(Nitrilotriacetate) complexes

The crystal structure of Na[Co(NC₆H₆O₆)] · H₂O is reported. The structure is compared to similar transition-metal nitrilotriacetate complexes containing different alkali cations and transition metals (Cu²⁺ and Zn²⁺). Inner-sphere coordination of the metals is similar, but the arrangement of counter-ions and water molecules in the unit cells vary with the size of the alkali cation.     

Kinetics of sulfur oxidation by thiobacillus ferrooxidans

Abstract

Thiobacillus ferrooxidans ATCC 23270 was grown with elemental sulfur as the energy source. Substrate oxidation was measured using a Clark‐type oxygen electrode. Whole cells demonstrated a broad pH optimum for sulfur oxidation between pH 2.0 and 8.0. The V _max and K_sfor sulfur oxidation varied depending on pH. Sulfite was oxidized at 227 nmol O₂/min/mg protein. Thiosulfate oxidation was slow, and tetrathionate oxidation was not detected. At a concentration of 2 mM, sodium azide completely inhibited sulfur, sulfite, and thiosulfate oxidation. Inhibition by N‐ethylmaleimide, antimycin A, and 2‐heptyl‐4‐hydroxyquinoline N‐oxide varied with substrate.     

Existence of aa 3-Type Ubiquinol Oxidase as a Terminal Oxidase in Sulfite Oxidation of Acidithiobacillus thiooxidans

It was found that Acidithiobacillus thiooxidans has sulfite:ubiquinone oxidoreductase and ubiquinol oxidase activities in the cells. Ubiquinol oxidase was purified from plasma membranes of strain NB1-3 in a nearly homogeneous state. A purified enzyme showed absorption peaks at 419 and 595 nm in the oxidized form and at 442 and 605 nm in the reduced form. Pyridine ferrohaemochrome prepared from the enzyme showed an α-peak characteristic of haem a at 587 nm, indicating that the enzyme contains haem a as a component. The CO difference spectrum of ubiquinol oxidase showed two peaks at 428 nm and 595 nm, and a trough at 446 nm, suggesting the existence of an aa ₃-type cytochrome in the enzyme. Ubiquinol oxidase was composed of three subunits with apparent molecular masses of 57 kDa, 34 kDa, and 23 kDa. The optimum pH and temperature for ubiquinol oxidation were pH 6.0 and 30 °C. The activity was completely inhibited by sodium cyanide at 1.0 mM. In contrast, the activity was inhibited weakly by antimycin A₁ and myxothiazol, which are inhibitors of mitochondrial bc ₁ complex. Quinone analog 2-heptyl-4-hydoroxyquinoline N-oxide (HOQNO) strongly inhibited ubiquinol oxidase activity. Nickel and tungstate (0.1 mM), which are used as a bacteriostatic agent for A. thiooxidans-dependent concrete corrosion, inhibited ubiquinol oxidase activity 100 and 70% respectively.     

Sulfite Oxidation Catalyzed by aa 3-Type Cytochrome c Oxidase in Acidithiobacillus ferrooxidans

Sulfite is produced as a toxic intermediate during Acidithiobacillus ferrooxidans sulfur oxidation. A. ferrooxidans D3-2, which posseses the highest copper bioleaching activity, is more resistant to sulfite than other A. ferrooxidans strains, including ATCC 23270. When sulfite oxidase was purified homogeneously from strain D3-2, the oxidized and reduced forms of the purified sulfite oxidase absorption spectra corresponded to those of A. ferrooxidans aa ₃-type cytochrome c oxidase. The confirmed molecular weights of the α-subunit (52.5 kDa), the β-subunit (25 kDa), and the γ-subunit (20 kDa) of the purified sulfite oxidase and the N-terminal amino acid sequences of the γ-subunit of sulfite oxidase (AAKKG) corresponded to those of A. ferrooxidans ATCC 23270 cytochrome c oxidase. The sulfite oxidase activities of the iron- and sulfur-grown A. ferrooxidans D3-2 were much higher than those cytochrome c oxidases purified from A. ferrooxidans strains ATCC 23270, MON-1 and AP19-3. The activities of sulfite oxidase purified from iron- and sulfur-grown strain D3-2 were completely inhibited by an antibody raised against a purified A. ferrooxidans MON-1 aa ₃-type cytochrome c oxidase. This is the first report to indicate that aa ₃-type cytochrome c oxidase catalyzed sulfite oxidation in A. ferrooxidans.     

Complete genome sequence of Desulfocapsa sulfexigens,a marine deltaproteobacterium specialized in disproportionating inorganic sulfur compounds

Desulfocapsa sulfexigens SB164P1 (DSM 10523) belongs to the deltaproteobacterial family Desulfobulbaceae and is one of two validly described members of its genus. This strain was selected for genome sequencing, because it is the first marine bacterium reported to thrive on the disproportionation of elemental sulfur, a process with a unresolved enzymatic pathway in which elemental sulfur serves both as electron donor and electron acceptor. Furthermore, in contrast to its phylogenetically closest relatives, which are dissimilatory sulfate-reducers, D. sulfexigens is unable to grow by sulfate reduction and appears metabolically specialized in growing by disproportionating elemental sulfur, sulfite or thiosulfate with CO₂ as the sole carbon source. The genome of D. sulfexigens contains the set of genes that is required for nitrogen fixation. In an acetylene assay it could be shown that the strain reduces acetylene to ethylene, which is indicative for N-fixation. The circular chromosome of D. sulfexigens SB164P1 comprises 3,986,761 bp and harbors 3,551 protein-coding genes of which 78% have a predicted function based on auto-annotation. The chromosome furthermore encodes 46 tRNA genes and 3 rRNA operons.     

Influence of Diesel Soot Particles and Sulfite on Functions of Polymorphonuclear Leukocytes

Aqueous suspensions of diesel soot particles in combination with sulfite influence certain functions of human polymorphonuclear neutrophils in vitro. Chemiluminescence, generated after activation by opsonized zymosan as well as oxygen uptake were decreased, whereas phagocytosis was increased. An enhancement of degranulation could not be observed. The single substances show little or no effects on the above properties. The results indicate that combinations of air pollutants such as diesel soot and sulfite may modulate vital functions of activated leukocytes in vivo.     

NADPH-dependent sulfite reductase flavoprotein adopts an extended conformation unique to this diflavin reductase

This is the first X-ray crystal structure of the monomeric form of sulfite reductase (SiR) flavoprotein (SiRFP-60) that shows the relationship between its major domains in an extended position not seen before in any homologous diflavin reductases. Small angle neutron scattering confirms this novel domain orientation also occurs in solution. Activity measurements of SiR and SiRFP variants allow us to propose a novel mechanism for electron transfer from the SiRFP reductase subunit to its oxidase metalloenzyme partner that, together, make up the SiR holoenzyme. Specifically, we propose that SiR performs its 6-electron reduction via intramolecular or intermolecular electron transfer. Our model explains both the significance of the stoichiometric mismatch between reductase and oxidase subunits in the holoenzyme and how SiR can handle such a large volume electron reduction reaction that is at the heart of the sulfur bio-geo cycle.     

Synergism among lactic acid, sulfite, pH and ethanol in alcoholic fermentation of Saccharomyces cerevisiae (PE-2 and M-26)

Summary The industrial production of ethanol is affected mainly by contamination by lactic acid bacteria besides others factors that act synergistically like increased sulfite content, extremely low pH, high acidity, high alcoholic content, high temperature and osmotic pressure. In this research two strains of Saccharomyces cerevisiae PE-2 and M-26 were tested regarding the alcoholic fermentation potential in highly stressed conditions. These strains were subjected to values up to 200 mg NaHSO₃ l⁻¹, 6 g lactic acid l⁻¹, 9.5% (w/v) ethanol and pH 3.6 during fermentative processes. The low pH (3.6) was the major stressing factor on yeasts during the fermentation. The M-26 strain produced higher acidity than the other, with higher production of succinic acid, an important inhibitor of lactic bacteria. Both strains of yeasts showed similar performance during the fermentation, with no significant difference in cell viability.